The white specimen, placed in spirit, yields a strong
solution of chlorophyl; the red, again, yields a red solution, which was
at once recognized as being tetronerythrin by my friend M. Merejkowsky,
who was at the same time investigating the distribution and properties
of that remarkable pigment, so widely distributed in the animal kingdom.
This substance, which was first discovered in the red spots which
decorate the heads of certain birds, has recently been shown by
Krukenberg to be one of the most important of the coloring matter of
sponges, while Merejkowsky now finds it in fishes and in almost all
classes of invertebrate animals. It has been strongly suspected to be an
oxygen-carrying pigment, an idea to which the present observation seems
to me to yield considerable support. It is moreover readily bleached
by light, another analogy to chlorophyl, as we know from Pringsheim's
researches.
When one exposes an aquarium full of _Anthea_ to sunlight, the
creatures, hitherto almost motionless, begin to wave their arms, as if
pleasantly stimulated by the oxygen which is being developed in their
tissues. Specimens which I kept exposed to direct sunshine for days
together in a shallow vessel placed on a white slab, soon acquired a
dark, unhealthy hue, as if being oxygenated too rapidly, although I
protected them from any undue rise of temperature by keeping up a flow
of cold water.
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